L9396 datasheet(72/109 Pages) STMICROELECTRONICS

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System functional safety implementations

L9396

72/109

DS12539 Rev 6

7.4.1

Watchdog (WD1)

The device and the microcontroller exchange queries and answers on a defined timing

base. An internal watchdog logic is implemented to inhibit load actuation such as to send

reset signal, while it can disable directly these drivers through a second switch-off path:

Pump Motor Pre-Driver

GPO Driver

Fail Safe Pre Driver

VBAT Switch

Figure 13. WD1 block diagram

Two modes of timing checks are provided:



Mono-directional: timing check based only on answers. Microcontroller must send

queries (without timing window check) and answers on a defined time window;



Bidirectional: timings are bidirectionally checked. L9396 must receive queries on a

defined time window. Microcontroller must send answers on a defined time window.

In case time windows are not respected an error is generated.

Figure 14. Mono-directional timing check evolution

SPI

Watchdog

Logic

Fault Counter

Logic

Configuration

GADG2401171253PS

WD1_RESET

(WD_CNT)

T_Answ_TimeOut

T_start_REQ

T_Valid_Answ_Start

T_Valid_Answ_End

Request

Answer

T_Req _TimeOut

T_Answ_TimeOut

T_start_REQ

T_Valid_Answ_Start

T_Valid_Answ_End

Answer

...

GADG2401171309PS

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